Sodium heated steam generator

ABSTRACT

A sodium heated steam generator in which the likelihood of tube failure from such factors as thermal growth is reduced and in which in the event of a tube failure the products of a sodium water reaction are quickly exhausted out of the steam generator. Water is generated to steam in bayonet tube assemblies extending downward into a vessel down through which liquid sodium flows and into which a central relief pipe extends to provide means for the escape of the products of an accidental sodium water reaction.

United States Patent 1191 Polcer et al.

SODIUM-HEATED STEAM GENERATOR Inventors: John Polcer, Florham Park;Robert 0. Barrett, Parsippany, both of N.J.; Allan E. Mu'sterer, LaJolla, Calif.

Foster Wheeler Corporation, Livingston, NJ.

Filed: Mar. 2, 1971 App]. No.: 120,154

Assignee:

US. Cl. 122/32, 122/483 Int. Cl. F221) 1/06 Field of Search 122/32, 34,483

; References Cited UNITED STATES PATENTS 4/1963 Bognar et a1. 165/142 xAmorosi et al. 165/142 X 1111 3,741,167 1 51 June 26, 1973 10/1966 Ammon122/483 X 3,613,781

7/1969 Barratt 122/32 Primary Examiner-Kenneth W. Sprague Attorney-JohnMaier, 11], Marvin A. Naigur and John E. Wilson [57] ABSTRACT A sodiumheated steam generator in which the likelihood of tube failure from suchfactors as thermal growth is reduced and in which in the event of a tubefailure the products of a sodium water reaction are quickly exhaustedout of the steam generator. Water is generated to steam in bayonet tubeassemblies extending downward into a vessel down through which liquidsodium flows and into which a central relief pipe extends to providemeans for the escape of the products of an accidental 'sodium waterreaction.

9 Claims, 4 Drawing Figures PATENTED JUNZB I975 SHEEI 1 BF 2 JOHN POLCERROBERT D. BARRATT ALLEN E. MUSTERER INVENTORS PAIENIEDJUHZG I975 I-SflEEI-2 N 2 INVENTORS JOHN POLCER ROBERT O. BARRATT ALLAN E. MUSTERERSODIUM-HEATED STEAM GENERATOR BACKGROUND OF THE INVENTION The mostfamiliar type of nuclear power plant utilizes liquid sodium to cool thereactor and to transfer heat to water to make steam. Such a systempresents a safety hazard because liquid sodium must be brought intoindirect heat exchange with water. In the event of a material failure,the liquid sodium and water could come into contact with the result ofan explosion due to the consequent sudden rise in pressure. Thepossibility of a liquid sodium reaction is ever present because of thethermal growth of the components in the steam generator and because ofthe erosion and corrosion which are concomitant with the use of flowingsodium. I

Still another problem found in sodium heated steam generators is theproblem of sodium stagnation caused by a lack of agitation in the sodiumflowing through the generator. The prevention of sodium stagnationincreases efficiency and reduces the chances of tube overheating andfailure.

SUMMARY OF THE INVENTION It is an object of the present invention toovercome the drawbacks found in the prior art such as those discussedabove. Accordingly, a sodium heated steam generator is provided with avertically extending elongated body in which a series of bayonet tubeassemblies are positioned to extend downward into the body of liquidsodium to bring water into indirect heat exchange with the sodium tomake steam. A central relief pipe extends down between baffles throughwhich the bayonet tube assemblies extend so that liquid sodium flowingdownward between the relief pipe and the side wall of the vessel flowsaxially inward and alternately outward across the bayonet tubes until itreaches the bottom of the vessel. In the event of an accidental sodiumwater reaction, the relief pipe is adapted to exhaust the product of thereaction quickly out of the vessel to prevent a violent explosion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a front view partly insection of a sodium heated steam generator made in accordance with thepresent invention;

FIG. 2 is a fragmentary view showing several of the bayonet tubes ofFIG. 1;

FIG. 3 is a top view partly in section taken substantially along theline 3--3 of FIG. 1; and

FIG. 4 is a top view partly in section taken substantially along theline 4-4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT There is shown in FIG. 1 asodium heated steam generator indicated generally as 10. It consists ofa pressure vessel 12 which is flared inwardly at 14 to provide a bottomand which has at its upper end a head section 16 with a lower flange 18which is connected to a flange 20 of the pressure vessel. The headsection 16 includes an annular chamber 22 which is defined by an innervertical wall 24 and an outer vertical wall 26 and an annular head 28which is secured to the top of the head section to completely enclosethe annular chamber 22. An annular upper tube sheet 30 extends acrossthe annular chamber 22, being secured at its marginal portions betweenthe head 28 and the tops of the inner vertical wall 24 and the outervertical wall 26. The upper tube sheet 30 divides the annular chamber 22into an upper chamber 32 and a lower chamber 34. The lower chamber 34 isdefined by the inner vertical wall 24, the outer vertical wall 26, theupper tube sheet 30, and a lower tube sheet 36.

Extending downwardly from the head section 16 and into the pressurevessel 12 are a series of bayonet tube assemblies 40. The bayonet tubeassemblies 40 comprise an inner tube 42 and an outer tube 44. Several ofthese assemblies are shown well in FIG. 2. Each of the inner tubes 42extends upwardly to the upper tube sheet 30. Each of the outer tubesextends upwardly to the lower tube sheet 36. Although the bottoms of thebayonet tube assemblies 40 are not shown in detail in the drawings, itwill be understood that the lower ends of the outer tubes 44 are closedwhile the lower ends of the inner tubes 42 extend almost to the ends ofthe outer tubes but are open. As shown in FIG. 2, spiral fins extenddown between the inner tube 42 and outer tube 44 of each of the tubeassemblies 40. This prevents departure from nucleate boiling, that isthe accumulation of steam pockets which create areas of little heatabsorption and consequent failure of the outer tubes. It has alreadybeen explained that it is necessary to prevent, as much as possible,tube failure which would result in a sodium water reaction.

A water inlet 48 allows water to enter the upper chamber 32 and flowdownwardly through the inner tubes 42 and to return upwardly between theinner tubes 42 and outer tubes 44 to be transformed into steam. Thesteam will collect in the lower chamber 34 and then flow out throughsteam outlets 50 for ultimate use as in a steam turbine.

The liquid sodium which is used to generate the steam is directed intothe pressure vessel 12 through a sodium inlet 52 and allowed to flowdownwardly through the pressure vessel 12 through a perforated flowdistribution sheet 54 to a lower chamber 56 and out of the pressurevessel 12 through a sodium outlet 58.

In order to insulate the pressure vessel 12 from the extremely hightemperatures of the incoming sodium a flow shroud 60 is provided. Theflow shroud 60 is generally cylindrical in configuration but has aninwardly flared bottom 62 which directs the downflowing sodium to thesodium outlet 58. As shown in FIG. 1, the

flow shroud 60 is spaced inwardly from the pressure vessel 12 andextends to a location slightly above the sodium inlet 52. Sodiumentering through the sodium inlet 52 will flow primarily upwardly overthe flow shroud but some of it will flow down between the flow shroud 60and the pressure vessel 12 to completely fill the space between thosetwo members. During operation this space will be completely filled withsodium which will insulate the pressure vessel 12 from the hightemperatures of the sodium being received by the steam generator 10.

The interior surface of the sodium inlet and most of the interiorsurface of the pressure vessel 12 are covered with a stainless steelliner 64 which in the event of a leak in the flow shroud 60 will delaythe sodium before it starts burning through the pressure vessel 12 for atime long enough for instrumentation to indicate the existence of theleak and emergency procedures to be executed. A suitable system would,for example, detect the presence of hydrogen which is released as theliquid sodium burns through thestainless steel liner 64. With adequatewarning the water and sodium in the generator can be withdrawn toprevent damage caused by the pressure created by a larger sodium waterreaction. The hot sodium flowing over the flow shroud 60 will flowdownward over the bayonet tube assemblies 40 in an inward andalternately outward flow path due-to a series of baffles.

In order to assure crossflow of the liquid sodium over the bayonet tubeassemblies 40, inner baffles 66 and outer baffles 68 are provided. Theinner baffles- 66 are spaced along thelength of the generatoralternately with the outer baffles 68. One of the outer baffles 68 isshown in plan in FIG. 3. It extends inwardly from the flow shroud 60 toa circle midway between the shroud and a central relief pipe 70 thefunction of which will be described presently. In order to assurerigidity, inwardly extending webs permit the outer baffles 68 to beconnected with the central relief pipe 70.

FIG. 4 shows one of the inner baffles 66. It is connected at a web 74 tothe central relief pipe 70 and extends outwardly to its periphery 76.The baffles 66 and 68 are connected with each other and with theperforated flow distribution sheet 54 and the lower tube sheet v36 bymeans of tie rods 80. The alternate-spacing of the inner baffles 66 andouter baffles 68 assures that the sodium will flow across bayonet tubeassemblies 40 throughout the length of its travel down the steamgenerator to the sodium outlet 58.

The bayonet tube assemblies 40 are not secured to the baffles 66 and 68but pass'through them loosely enough to permit the bayonet tubeassemblies to expand and contract without imparting stresses to thesurrounding structure. The use of bayonet tubes which are secured onlyat one of their ends to a tube'sheet and which are slidably secured tothe baffles which are secured by a tiered only at one end to a fixedtube sheet has minimized the thermal growth problems which in manysodium'hea'ted steam generators create the hazard of tube failure andits consequent sodium water reaction.

It has already been explained that in spite of precautions such as thosediscussed above, tube failure and consequent sodium waterreaction is anever present possibility. In order to relieve the present steamgenerator of the products of such a reaction andthereby eliminate thepossibility of an explosion, the central relief pipe 70 which is closedat its lower end 81 has a series of burst disks 82 which in the-event ofa sodium water reaction rupture to allow sodium through the relief pipe70 and flow upwardly unobstructed to a location where it can be safelytreated. in order to prevent the burst disks 82 from rupturinginadvertently and to prevent a reaction between oxygen and/or air withliquid sodiuin, the inside of the central relief pipe 70 is filled withan inert gas maintained at a suitable pressure.

After flowing through the perforated flow distribution sheet 54, theliquid sodium flows through the annular lower'chamber 56 between theinwardly flared bottom section 62 of the flow shroud 60 and the centralrelief pipe 70 until it reaches the sodium outlet 58 and thereafterpasses out of the steam generator 10.

The outgoing sodium flows through a ferrule 84 positioned within thesodium outlet 58. The sodium in the annular space between the' bottom 14of the pressure vessel and the inwardly'flared bottom 62 of the flowshroud 60 is restrained from moving into the sodium outlet by bellows86. The bellows 86 extend downward from the inwardly flared bottom 62 toa flange 8 8 which is urged downward against a seat 90 on the bottom 14of the pressure vessel 12 by spring 92. This creates a seal and permitsthe insides that is the entire generator 10 other than the shell 12, andits bottom 12, to be lifted out for inspection or repair withoutbreaking any parts at the lower seal. Similarily the insides can belowered into place and will seal at the seat 90 because the spring 92will urge the flange 88 against the seat 90.

Thesteam generator is supported by supports 94 which are connected at alocation fairly high on the steam generator 10 to prevent it fromtoppling even in the event of an earthquake. To prevent the steamgenerator from swinging in such an eventuality the steam generator canbe supported laterally in the vicinity of the perforated flowdistribution sheet 54. The sheet 54 will transmit forces receivedexternally about the shell '12 and flow shroud 64 through projections 96which project radially outward from the flow shroud 64 toward the shell12. The projections 96 do not contact the shell 12 but in the event thatan excessive external lateral force should be exerted in the vicinity ofthe perforated flow distribution sheet, the projection 96 and shell 12will make contact to distribute the force and avoid a catastrophiccollapse of the generator 10.

The-foregoing describes but one preferred embodiment of the presentinvention. Other embodiments are possible and modifications can be madewithout exceeding the scope of the present invention as defined in thefollowing claims.

What is claimed is:

l. A sodium heated steam generator comprising an elongated verticallyextending pressure vessel, a plurality of bayonet tube assembliesextending longitudinally of and within said pressure vessel, saidbayonet tube assemblies each having an outer tube closed at its lowerend and open at its upper end and an inner tube open at both endspositioned within said outer tube, an upper tube sheet and a lower tubesheet, said inner tubes extending to said upper tube sheet, said outertubes extending to said lowertube sheet, a water inlet above said upper.tube sheet anda steam outlet between said upper tube sheet and saidlower tube sheet, a liquid sodium inlet below said lower tube sheet anda liquid sodium outlet at the lower portion of said generator, meanslocated along the longitudinal axis of said generator for releasing theproducts of an accidental sodium water reaction, said bayonet tubeassemblies being positioned radially of said means, a plurality ofannular baffles extending outwardly from said means with said bayonettubes extending loosely through said baffles, said baffles includinginner baffles permitting sodium to flow downward in substantial quantityonly when spaced from said means, and outer baffles spaced alternatelywith-respect to said first defined baffles and permitting said sodium toflow downwardly only when adjacent to said means. a

2. The steam generator defined in' claim 1 wherein said other baffleshave a plurality of webs extending inwardly to said means the spacesbetween said webs permitting said sodium to flow downwardly.

3. The steam generator defined in claim 2 further 1 comprising aplurality of tie rods secured to said lower tube sheet and extendingdownwardly through said baffles, said baffles being connected to saidtie rods.

4. The steam generator defined in claim 3 further comprising a flowshroud, said flow shroud extending vertically and spaced outwardly fromsaid means, the upper end of said flow shroud extending above saidsodium inlet so that sodium flowing into said generator through saidinlet will flow upwardly over said shroud and then downwardly over saidbaffles and said bayonet tube assemblies.

5. The steam generator defined in claim 4 further comprising a pressurevessel, said flow shroud being positioned within said vessel with asmall vertical annular space between said shroud and said vessel so thata portion of said sodium coming through said sodium inlet will flowdownward in said space until said space is filled with sodium.

6. The steam generator defined in claim 5 wherein said outer baffles arejoined at their outer periphery with said flow shroud.

7. The steam generator defined in claim 6 wherein said means is acentrally positioned relief pipe with a plurality of openings spacedlongitudinally thereof and a burst disk bridging each of said openingsand adapted to rupture at a predetermined pressure to allow the productsof a liquid sodium reaction to enter said relief pipe and be directedout of said generator.

8. The steam generator defined in claim 7 wherein said flow shroud andpressure vessel are flared inwardly at the bottoms thereof and furthercomprising a ferrule extending downwardly from the bottom of said flowshroud to direct sodium to said sodium outlet, a bellows extendingdownwardly from the bottom of said shroud to a flange, and a springpositioned between said flow shroud and said flange to urge said flangedownwardly against the bottom of said pressure vessel.

9. The steam generator defined in claim 8 further comprising a flange onsaid bottom of said pressure vessel adapted to be engaged by said firstdefined flange.

1. A sodium heated steam generator comprising an elongated verticallyextending pressure vessel, a plurality of bayonet tube assembliesextending longitudinally of and within said pressure vessel, saidbayonet tube assemblies each having an outer tube closed at its lowerend and open at its upper end and an inner tube open at both endspositioned within said outer tube, an upper tube sheet and a lower tubesheet, said inner tubes extending to said upper tube sheet, said outertubes extending to said lower tube sheet, a water inlet above said uppertube sheet and a steam outlet between said upper tube sheet and saidlower tube sheet, a liquid sodium inlet below said lower tube sheet anda liquid sodium outlet at the lower portion of said generator, meanslocated along the longitudinal axis of said generator for releasing theproducts of an accidental sodium water reaction, said bayonet tubeassemblies being positioned radially of said means, a plurality ofannular baffles extending outwardly from said means with said bayonettubes extending loosely through said baffles, said baffles includinginner baffles permitting sodium to flow downward in substantial quantityonly when spaced from said means, and outer baffles spaced alternatelywith respect to said first defined baffles and permitting said sodium toflow downwardly only when adjacent to said means.
 2. The steam generatordefined in claim 1 wherein said other baffles have a plurality of websextending inwardly to said means the spaces between said webs permittingsaid sodium to flow downwardly.
 3. The steam generator defined in claim2 further comprising a plurality of tie rods secured to said lower tubesheet and extending downwardly through said baffles, said baffles beingconnected to said tie rods.
 4. The steam generator defined in claim 3further comprising a flow shroud, said flow shroud extending verticallyand spaced outwardly from said means, the upper end of said flow shroudextending above said sodium inlet so that sodium flowing into saidgenerator through said inlet will flow upwardly over said shroud andthen downwardly over said baffles and said bayonet tube assemblies. 5.The steam generator defined in claim 4 further comprising a pressurevessel, said flow shroud being positioned within said vessel with asmall vertical annular space between said shroud and said vessel so thata portion of said sodium coming through said sodium inlet will flowdownward in said space until said space is filled with sodium.
 6. Thesteam generator defined in claim 5 wherein said outer baffles are joinedat their outer periphery with said flow shroud.
 7. The steam generatordefined in claim 6 wherein said means is a centrally positioned reliefpipe with a plurality of openings spaced longitudinally thereof and aburst disk bridging each of said openings and adapted to rupture at apredetermined pressure to allow the products of a liquid sodium reactionto enter said relief pipe and be directed out of said generator.
 8. Thesteam generator defined in claim 7 wherein said flow shroud and pressurevessel are flared inwardly at the bottoMs thereof and further comprisinga ferrule extending downwardly from the bottom of said flow shroud todirect sodium to said sodium outlet, a bellows extending downwardly fromthe bottom of said shroud to a flange, and a spring positioned betweensaid flow shroud and said flange to urge said flange downwardly againstthe bottom of said pressure vessel.
 9. The steam generator defined inclaim 8 further comprising a flange on said bottom of said pressurevessel adapted to be engaged by said first defined flange.